In the apparatus for sintering the fuel pellets in the nuclear fuel producing process, it is necessary to maintain or retain containment for handling a nuclear fuel substance. The continuous sintering apparatus of the prior art is made to have a joint structure in which the furnace casing can be divided into a plurality of (e.g., three or so) blocks. By sandwiching O-rings or the like between the individual furnace casing blocks, gas-tightness is maintained. Moreover, an entrance glove box and an exit glove box are connected to the two ends of the furnace casing. The entrance glove box and the exit glove box are connected at the two ends of the furnace casing to maintain containment by O-rings and flanges.
The ordinary sintering operations are performed by the following procedure. The pellets to be sintered are delivered on a dedicated truck from a preceding step to the entrance glove box to pass through the furnace casing while being carried on a tray. During this passage, the pellets are subjected to a sintering treatment. The sintered pellets are then sequentially delivered out to the exit glove box and transferred on a dedicated truck to a succeeding step.
The use of such a sintering apparatus for a long period of time causes damage or deterioration of the furnace members in the furnace casing such as heaters or insulating bricks. At a periodic interval or at occurrence of problems, therefore, the furnace casing or furnace members have to be inspected, repaired or replaced. In order to repair or replace the furnace members such as the heaters or the insulating bricks, however, the furnace casing blocks have to be separated, and the containment cannot be maintained during separation of the furnace casing blocks.
Therefore, in the maintenance method of the prior art, a greenhouse (i.e., a simple facility such as a tent which is enveloped with a vinyl sheet so as to maintain gas-tightness between the inside and outside and is bound at a suitable site to a metal frame so as to keep its shape) is installed around the continuous sintering furnace, so that a worker wearing protective clothing such as a flight suit enters the greenhouse to perform the necessary operations. More specifically, when the furnace member is to be replaced, the furnace casing blocks are jointed at first with a furnace casing block separating vinyl bag, and the furnace casing block to be maintained is separated and subjected to the maintenance operations in the greenhouse.
Thus, in the prior art, it is necessary to install the greenhouse around the continuous sintering furnace and to equip the greenhouse with an exhaust system for maintaining a negative pressure. This necessity enlarges the facilities required for maintenance and causes a problem that it takes a long time to install or remove the greenhouse. As a result, a wide space is required for the installation, and the sintering apparatus have to be shut down for a long period of time for maintenance and repair.
Moreover, the worker has to enter the greenhouse to perform the operations while wearing protective clothing, and the furnace casing blocks have to be jointed with cylindrical vinyl bags so that they may be separated. This raises a problem that the operations are complex and take a long time.